Description

Privilege escalation in the WebDriver BiDi component. This vulnerability was fixed in Firefox 155.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "8.8",
  "pubDate": "2026-09-01T13:20:06.763Z",
  "pubdate": "2026-09-01T13:20:06.763Z",
  "executiveSummary": "A privilege escalation vulnerability has been identified within the WebDriver BiDi component of the Mozilla Firefox browser. This security flaw allows a malicious actor to bypass security boundaries by leveraging the bi-directional communication protocol inherent in the WebDriver BiDi architecture.\nThe vulnerability represents a significant risk to system integrity and user data confidentiality, as it potentially enables unauthorized elevation of privileges beyond the standard sandboxed execution environment of the browser. By exploiting the communication channel between the WebDriver client and the browser, an attacker can execute arbitrary code or interact with sensitive APIs that are typically restricted from content-level access.\nThe flaw affects all versions of Firefox prior to the release of Firefox 155. Successful exploitation necessitates a target configuration where the WebDriver BiDi interface is either accessible or can be triggered via a malicious web page or local manipulation. Users are advised to upgrade to Firefox 155 or newer immediately to mitigate the risk of exploitation. This vulnerability underscores the inherent risks associated with automated browser control interfaces if they lack sufficient isolation and input validation.",
  "technicalDetails": "The vulnerability resides within the WebDriver BiDi component, a protocol designed to provide real-time, bi-directional communication between the browser engine and WebDriver clients. Unlike the traditional WebDriver protocol, which relies on synchronous command-response cycles, BiDi introduces event-driven capabilities and closer integration with the browser's internal event loops.\nThe root cause of this privilege escalation stems from insufficient security boundaries and inadequate validation of messages transmitted through the BiDi connection. When the browser processes commands via the WebDriver BiDi interface, the logic responsible for command dispatching fails to strictly enforce the principle of least privilege, allowing commands that should be reserved for privileged or chrome-level contexts to be invoked by potentially untrusted sources.\nThe attack flow begins when an attacker establishes a connection or interacts with the WebDriver BiDi interface. In many scenarios, this involves the exploitation of a secondary vulnerability that allows the injection of commands into the browser's internal automation handlers. Once the attacker gains the ability to send requests to the BiDi component, they can construct malicious payloads designed to interact with internal browser functions that bypass standard sandbox restrictions. By exploiting the trust relationship between the BiDi handler and the browser's core engine, the attacker can force the browser to perform operations with elevated privileges.\nBecause the WebDriver BiDi component is tightly integrated into the browser's execution path, the exploitation of this vulnerability can result in the circumvention of Content Security Policies (CSP) and Cross-Origin Resource Sharing (CORS) restrictions. Furthermore, if the browser is running with inherited system-level permissions, a successful exploit may lead to full system compromise by enabling arbitrary file system access or remote code execution outside the browser's restricted container.\nThe vulnerability is fixed in Firefox 155, where Mozilla developers implemented stricter origin checks and enhanced message validation for all incoming WebDriver BiDi requests. Prior to this patch, the lack of rigorous authentication and session authorization meant that any entity capable of communicating with the BiDi socket could theoretically issue commands that lead to privilege escalation. The remediation involved refactoring the command-handling dispatch table to ensure that sensitive internal APIs are explicitly protected from non-privileged BiDi client calls."
}